Step 3 will be initiated at least 4 weeks after the completion of the Step 2 safety follow up visit (Visit 4). If greater than 60 days elapse between Visit 4 and Visit 5, participants will repeat screening Visit labs to qualify for continued study participation. In Step 3, two paired doses of VOR 400 mg will be administered. The interval between the 2 paired doses can be as short as 48 hours (2 days), and as much as 96 hours (4 days) apart from each other. Participants were assessed for in vivo response via a 3rd leukapheresis after the second of the paired doses of 400 mg VOR. The first three (3) participants will first be assessed for an in-vivo response after the 2nd dose of the paired doses given 48 hours (2 days) apart. Subsequent participants will be assessed for responses to paired doses separated by 48 hours, or the interval may be lengthened to as much 96 hours (4 days), as dictated by the accumulated responses observed in subsequent participants.